A number of sulfide mineral-thiol collector interactions have been identified as electrochemical or electron transfer processes. Laboratory studies have confirmed that these interactions can be controlled by variation of the mineral potential, using either a directly applied potential or redox-controlling reagents to induce or depress flotation. Control of the mineral potential in the laboratory has proved to be a very precise means of achieving flotation. If similar results can be achieved on a commercial scale, more efficient recovery of domestic critical and strategic minerals might be possible. To develop an understanding of the relationship between redox potential and recovery in commercial flotation plants, a portable system for in situ monitoring of the pulp conditions in sulfide flotation circuits has been developed. The multichannel capability of this data acquisition system provides for the simultaneous monitoring of redox potentials on a variety of metal and mineral electrodes. The system also provides for the monitoring of such parameters as ph, dissolved oxygen content, and soluble ion concentration. The results of probe tests at two commercial processing plants will be discussed in terms of the differences in mineral and metal electrode potentials under similar conditions; the effects of reagent, ph, and dissolved oxygen on these potentials; and the viability of using potential as a commercial flotation control parameter.